Software on a computer system can be logically divided into three levels, including an operating system level, a control level, and an application level. The operating system level includes software that interfaces with the hardware components of the computer and performs rudimentary tasks such as the control and allocation of memory, central processing unit time, disk space, and peripheral devices. One popular example of software residing at the operating system level is the WINDOWS® brand operating system, which was developed and distributed by Microsoft Corporation of Redmond, Wash.
The control level is positioned on top of the operating system level and includes software that manages various control elements of a graphical user interface. For example, software at the control level can implement standard user interface control elements such as buttons, which allow a user of the computer system to select options, as well as scroll bars, which allow the user to move through text in a document.
The application level resides on top of the control level and includes software that is divided into various applications. An application is a program designed to assist a user in the performance of a specific task. An example of an application at the application level is a word processing application, such as the WordPad application provided as an accessory application to various versions of the WINDOWS® brand operating systems.
An application can include a plurality of control elements, which are implemented at the control level. Commanding is implemented globally across all control elements for a particular application. Therefore, because commanding for the control elements is implemented at the control level, commanding is handled identically across all control elements regardless of which control element receives a given input sequence.